1. Field of the Invention:
This invention relates to steam turbine apparatus and in particular to a damping device for limiting motion between adjacent nozzle chambers and between nozzle chambers and the interior of the turbine casing in both the axial direction and in a plane transverse thereto.
2. Description of the Prior Art:
As is known to those skilled in the art of steam power generation, a turbine apparatus comprises a casing having a plurality of annular arrays of stationary blades mounted therein and a rotor member having a corresponding plurality of annular arrays of rotating blades interposed between each array of stationary blades. A motive fluid, commonly steam, is confined and guided within the turbine casing and passes over the stationary and rotating blades to convert the energy of the high temperature, high pressure steam into rotational mechanical energy.
The casing is a substantially cylindrical member cast of suitable material and has disposed circumferentially about the interior thereof a plurality of interlocked nozzle chamber members. The nozzle chamber members form the mounting on which a plurality of nozzle blocks are placed. These nozzle blocks convey steam from the inlet piping extending through the casing and introduce that steam onto the first array of rotating blades mounted on the rotor disposed within the casing.
Each nozzle chamber is itself an arcuate member that is mounted, by a tongue-and-groove fit, on the interior of the turbine casing. Each nozzle chamber is itself engaged with the adjacent nozzle chamber through a similar tongue-and-groove fit.
Recent failures of several on-line turbine units have led to the discovery of excessive fit clearance between the tongue-and-groove fits disposed between adjacent nozzle chambers and between the nozzle chambers and the turbine casing. These tongue-and-groove fits are provided to prevent displacement of the engaged nozzle chambers in the axial direction within the turbine casing and to resist vibration, by frictional engagement, in a plane transverse to the turbine axis. At the same time, however, the tongue-and-groove fit allows thermally-caused relative motion to occur in the transverse plane. As a general rule, the total initial clearance at fitting between each tongue-and-groove fit, whether between adjacent nozzle chambers or between a nozzle chamber and the interior of the casing, is approximately 0.003 inches.
In the course of time and during operation of the apparatus, vibration of the nozzle chamber in both the axial direction and in the transverse plane results in substantial wear of the surfaces of the tongue-and-groove fits. Such wear increases the initial clearance and renders the tongue-and-groove fits ineffective for restricting axial displacement of the nozzle chambers relative to the turbine casing and in damping any vibration of the nozzle chambers.
It is apparent that a damping device which will limit motion of the nozzle chambers in the axial direction relative to the turbine casing and which will limit motion of adjacent nozzle chambers relative to each other in a transverse plane is required.